1. Field of the Invention
The present invention relates to chlorine resistant amide polymers and to membranes made from such and to methods of using said polymers and membranes.
2. Description of the Related Art
The desalting membrane of choice worldwide is a polyamide (PA) membrane. PA membranes are made by forming a thin PA film on a finely porous surface of a polysulfone (PS) supporting membrane by an interfacial reaction between the reactant pair trimesoyl chloride (TMC) and m-phenylenedimaine (MPD). The following equation illustrates the chemical formation of a PA desalination barrier:

In the above equation, the first term represents m-phenylenediamine in water, the second term represents the trimesoyl chloride in hydrocarbon, and the resultant term represents the fully aromatic polyamide thin film. This is the equation for the PA thin-film composite membrane developed by Cadotte and E. E. Erickson (Desalination, Volume 32, 25-31, 1980) and, as indicated above, is the membrane in common use throughout the world.
A great need exists to improve the stability of the present state-of-the-art membranes used for chlorine disinfection. Such improvement is critical, for example, in reverse osmosis (RO) plants operating on wastewaters, surface waters, and open seawater intakes wherein disinfection by chlorination is required to control the growth of microorganisms (so-called biofouling) on the surface of the membrane. These PA membranes are so susceptible to deterioration by chlorine that a dechlorination step is required when chlorine is used as a disinfectant in the pretreatment. It will be understood that dechlorination prior to the PA membrane creates additional costs and effectively nullifies disinfection on the membrane surface where disinfection is needed. It is also noted that such dechlorination does not neutralize all chlorine, and the small amount of residual chlorine shortens membrane life.
U.S. Pat. No. 7,806,275 (Murphy et al) teach chlorine resistant polyamides modified with electron-withdrawing groups are useful to make PA membranes, useful in desalination units, that exhibit sufficient activity to minimize any chlorination on both the amine and acid chloride side and minimize N-chlorination. The patent states that attempting to add electron-withdrawing groups to the amine side of the membrane would create a number of problems including: (1) difficulties in obtaining precursors and overall synthesis; (2) an increase in electron-withdrawing away from the nitrogen; (3) resonance problems resulting in ring chlorination; (4) water solubility problems arising from the addition of hydrophobic groups; (5) less reactivity during interfacial polymerization; and (6) all successful membranes made based on amine modification show problems with flux.
While there are various PA membranes useful for desalination, there still remains a need in the art for a more effective membrane that is more tolerant to chlorine. The present invention, different from prior art systems, provides such a membrane that is useful, for example, for desalination.